I am too old to have many heroes left but one I retain is Hugh Thompson. He is an unlikely hero for someone of my political disposition: a conservative southern Baptist who volunteered to fight for the US in the Vietnam War.

On March 16th, 1968, Thompson was flying his reconnaissance helicopter above the village of My Lai when he began to spot groups of bodies. He hovered over one young woman who was injured and signalling for help. He watched, appalled, as an American officer prodded her with his foot and then finished her off. He then saw heaps of human corpses in an irrigation ditch. Images of Nazi atrocities in the second World War came to his mind.

Thompson saw a group of about 10 villagers, some of them children, running from a platoon of soldiers.

He landed his helicopter between the villagers and the soldiers and then committed an act of gross treason: he ordered his machine gunner to open fire on their fellow Americans if those soldiers fired on the villagers. His exact words were: “Open up on ’em; blow ’em away.”

Thompson’s actions forced other helicopters to land and begin ferrying wounded civilians to safety. His actions stopped the massacre. Thompson was subsequently a key figure in the defiance of the organised official cover-up of the My Lai atrocity in which American soldiers had murdered more than 400 innocent civilians, many of whom were also raped and mutilated. His commanders sent him on increasingly dangerous missions – many wanted him dead.

Thompson was, by the official standards of the time, a serious threat to his country. He had openly threatened to kill US troops. And his subsequent role in revealing the truth about My Lai did immense damage to US interests. It was of enormous propaganda value to the enemies of the US in Vietnam and around the world.

Yet, with time, Americans generally came to see Thompson as the one who embodied their deepest values. In 1998, he was awarded one of the army’s highest honours, the Soldier’s Medal. The citation said: “Thompson’s heroism exemplifies the highest standards of personal courage and ethical conduct.”

This about-face was not entirely hypocritical. Thompson, who died in 2006, was a deeply American figure. There is nothing as American as individual conscience.

Largely because of its roots in dissenting Protestantism, the US has long been defined by the defiance of overweening authority. It is, after all, a country founded by those, such as Thomas Jefferson, who asked: “What country can preserve its liberties if their rulers are not warned from time to time that their people preserve the spirit of resistance?”

The American spirit is best expressed in outrageous acts of political law-breaking: William Lloyd Garrison burning a copy of the constitution because it did not outlaw slavery; Henry David Thoreau going to prison for refusing to pay his poll tax because his home state, Massachusetts, had voted to return fugitive slaves to their masters; Susan B Anthony arrested for voting (illegally for a woman) in the 1872 presidential election; Rosa Parks refusing to sit at the back of the bus; Martin Luther King getting himself arrested for demanding service in a whites-only restaurant – all of these were illegal acts and all of them are now seen as crucial expressions of the US’s better self.

Thoreau’s essay Civil Disobedience is as central an American text as the declaration of independence or the constitution. It proclaims, among other things, that “If the machine of government is of such a nature that it requires you to be the agent of injustice to another, then, I say, break the law”. Hugh Thompson would have agreed heartily. So, surely, would Bradley Manning.

What is the difference between Bradley (now Chelsea) Manning and Hugh Thompson? Not very much, especially if you take into account the shift in the conduct of war from the personal to the digital since 1968. Both, as it happened, were spurred by the same thing: the view from a helicopter of American troops massacring civilians. Thompson saw it happening directly. Manning saw graphic video of a US Apache helicopter gunship killing a group of innocent people in Baghdad.

Thirty years on from My Lai, Thompson gave Americans comfort in the knowledge that at least someone had shouted stop. In 30 years’ time, Manning may be seen in the same light.

Last week’s savage 35-year prison sentence on Manning is an attack on the great American tradition of civil disobedience. It is especially ironic that this assault comes under a president who owes everything to that tradition: if Rosa Parks and Martin Luther King had not placed their consciences above the law, there would be no President Barack Obama.

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